From the electrophysiologist's point of view, striate cortex remains one of the outstanding examples of information processing in the CNS. It is built on a principle of multiple, independent modules and displays a wide variety of receptive field(RF) types which differ from those of its afferent input in many ways. How these RFs are synthsized has been the object of much debate but remains obscure. In the proposed research we will take rather direct attacts on the functional organization of the RFs of one class of striate neuron, the simple cell. The major part of the proposed research will consist of simulaneously recording from cortical cells and retinal ganglion cells. Retinal excitatory and inhibitory drives of cortical cells will be identified on-line by computation of cross-correlograms. Precise spatio-temporal maps of pairs of connected cells will be generated with both moving and stationary stimuli. These, plus the sign of the connection, will go far to answer fundamental questions about the mapping if X, Y and W retinal afferents onto particular classes of cortical cells and will permit specification of the role or these afferents in the synthesis of striate RFs. In addition, we plan to study the role of inhibition in the organization of the simple RF. This will be achieved by intracellular recording in simple cells and by voltabe clamp accompanied by specific visual stimulations sequences. Finally, we will further explore the properties of a new class of simple cells, those with many, periodically spaced excitatory regions. This exploration will be performed in both the space and spatial frequency domains and we will prusue our suspicion that these are output cells sending axons to extrastriate cortex.